1. Field of the Invention
The present invention relates to a radio-frequency composite element having an amplifier and a nonreciprocal circuit element mounted integrally on a circuit board, the amplifier including a semiconductor amplifier such as an FET or a transistor arrangement or by a high-efficiency amplifier used particularly in mobile communication devices or microwave communication instruments.
2. Description of the Related Art
FIG. 28 schematically shows a conventional radio-frequency circuit device.
In FIG. 28, reference numeral 200 denotes a radio-frequency circuit device making up part of a transmitter used in radio equipment typically represented by a conventional portable terminal apparatus. Reference numeral 202 stands for an isolator; 204 for a high-efficiency amplifier; 204a for a main body of the high-efficiency amplifier; 204b for a cover that envelops the body 204a; 206 for a transmission line connecting the isolator 202 with the high-efficiency amplifier 204; and 208 for a circuit board. Although not shown, other circuit elements, in addition to the high-efficiency amplifier 204 and isolator 202, are also connected with the transmission line 206 on the circuit board 208.
Mobile communication devices utilize a nonreciprocal circuit element typically represented by the isolator 202 in order to operate the high-efficiency amplifier 204 efficiently regardless of the state of the antenna.
A signal is input through an input terminal (not shown) of the high-efficiency amplifier 204 and is amplified by the latter. The amplified signal is forwarded over the transmission line 206 and through the isolator 202 before being output from an output terminal (not shown) of the isolator 202. Any reflected wave from downstream of the output terminal of the isolator 202 is shielded by the latter and will not return to the high-efficiency amplifier 204. This allows the amplifier 204 to operate in a significantly efficient and stable manner.
Portable terminal apparatuses have been getting smaller and lighter than ever in recent years. Efforts to make things more compact and lightweight constitute an important factor in developing a portable terminal apparatus. A battery kit of the apparatus is a component that, if reduced in size, contributes significantly to making the portable terminal apparatus smaller and lighter.
However, the battery size can be reduced only so much; simply diminishing the battery dimensions will end up failing to ensure an adequate time period for making calls. Other circuit components must be made more efficient so as to save as much power as possible in the portable terminal apparatus. Of the remaining components, the amplifier consumes an appreciably large portion of power. It is thus important to boost the efficiency of the amplifier as part of the effort to reduce power dissipation.
Generally, the output impedance of the high-efficiency amplifier 204 is 50 ohms and so is the input impedance of the isolator 202. The characteristic impedance of the transmission line 206 between the two components is set to the 50-ohm level so as to minimize the line loss and to save power consumed by the high-efficiency amplifier 204.
As portable terminal apparatuses are getting thinner and smaller today, the circuit board 208 tends to be lessened in thickness correspondingly. If the characteristic impedance of the transmission line 206 were to be held at 50 ohms, the line 206 would have to be made narrower. This would lead to characteristic impedance variations of the transmission line 206 between different apparatuses. Such impedance variations, combined with deviations in the output impedance of the high-efficiency amplifier 204 and in the input impedance of the isolator 202, would disrupt impedance matching among the components. As a result, the line loss would increase and little saving could be made on the power dissipation of the high-efficiency amplifier 204.
The simplest solution to the above problem involves giving wider margins to the specifications of the high-efficiency amplifier 204, isolator 202, and the circuit board 208 including the transmission line 206. One disadvantage of the solution, however, is an increase of cost.
In this connection, circuit board designers have been prompted to work out a more accurate impedance design of the transmission line. The need to acquire such a design feature has prolonged the period of development.
Another solution to the problem described above is proposed in Japanese Patent Laid-open No. Hei 10-327003. This application discloses a setup in which an isolator with an impedance-matching circuit built therein is incorporated into a transmitting amplifier. An output terminal of an output amplifying element in the transmitting amplifier is connected to the isolator by way of a low-impedance transmission line. The setup helps enlarge a microstrip line regardless of the circuit board being made thinner so as to eliminate impedance mismatch, whereby the line loss is minimized.
This proposed setup still uses the ordinary circuit board. As one disadvantage of the setup, enlargement of the microstrip line, irrespective of the thin circuit board can impede efforts to reduce the surface area of the circuit board.
The isolator is mounted on the circuit board of the transmitting amplifier. Among the circuit components, the isolator has a prominent elevation and will suffer characteristic deterioration if reduced significantly in height. It follows that thinning the transmitting amplifier can be difficult to accomplish as long as the isolator incorporated in the transmitting amplifier is mounted on the latter""s circuit board.
It may be added that demands are higher than ever for cellular phones working as portable terminal apparatuses to be smaller as well as thinner. Illustratively, of the mobile phones being marketed in Japan, some are as thin as 15 mm or even less. Every time a new model comes out, a millimeter or so is shaved off its thickness. This has entailed a strong demand for making thinner each of the components constituting the cellular phone. One of the thickest electronic parts mounted on the circuit board of the cellular phone is the isolator. At present, the isolator is about two millimeters thick. What is being demanded today is for the isolator thickness to be shaved in increments of 0.1 mm without degrading the electrical characteristics of the isolator.
Japanese Patent Laid-open No. Hei 9-270608 discloses a transmitter-receiver comprising a circuit having an isolator mounted on the amplifier output side.
Japanese Patent Laid-open No. 2000-58977 depicts an optical radio-frequency communication unit in which a low-speed control signal circuit and a radio-frequency signal circuit are mounted on separate circuit boards in a single package. The circuit boards are each equipped with a shield to prevent interference, and the radio-frequency signal circuit is designed to optimize its characteristic impedance to improve transmission characteristics.
Furthermore, Japanese Patent Laid-open No. Hei 9-8584 describes a setup in which circuit elements of a sending filter and a branching filter for use illustratively by a cellular phone are implemented in the form of conductive patterns on a multilayer substrate or of chip parts, with a SAW filter adopted as a receiving filter mounted on the multilayer substrate.
The present invention has been made to overcome the above and other deficiencies of the prior art and it is an object of the invention to provide a radio-frequency composite element for constituting integrally by an amplifier and a nonreciprocal circuit element, and being small and thin in size and easy to mount on a circuit board.
A radio-frequency composite element according to invention comprising: an amplifying element constituted by a body made of a multilayer substrate and of a semiconductor element attached to the multilayer substrate, and by a cover covering the body; a nonreciprocal circuit element constituted by a body assembly made of a magnetic material, of a plurality of central electrodes surrounding the magnetic material while being isolated from one another, and of a magnet applying magnetic fields to the magnetic material and the central electrodes; and by a shield shielding the body assembly; and a first connective conductor for connecting an output terminal of the amplifying element with an input terminal of the nonreciprocal circuit element.
Accordingly, the present invention is advantageous that this structure forms a small-sized amplifying element that is located adjacent to the nonreciprocal circuit element, the two components being held together in an integral fashion so that the resulting radio-frequency composite element is made thinner and smaller than ever.
Other objects and advantages of the invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific embodiments are given by way of illustration only since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.